Pulsed and continuous wave (CW) chemically-pumped lasers were invented in the l960s. All currently known lasers of this class operate well into the infrared spectrum, a prominent example being the hydrogen-fluoride (HF) and deuterium fluoride (DF) lasers. Despite an intensive effort, however, the discovery of a chemically-pumped visible laser has eluded the research community. For example, Cobb et al, in Chemical Physics Letters, 143(3), pp. 205-213 (1988) has recently measured a positive value for the small signal gain on electronically excited diatomic sodium, Na.sub.2, vapor. In Cobb, liquid sodium is vaporized in an oven with the vapor escaping through a small orifice into the very low pressure chamber of a molecular beam device. In the early part of the rapid vapor expansion, some of the sodium vapor in Cobb forms small molecular clusters. This polymerization process terminates in a vapor jet when the vapor density becomes too low for further collisions. A separate stream of monatomic halogen atoms is introduced into the low pressure chamber. A portion of these atoms becomes entrained in the sodium vapor jet and reacts with some of the sodium trimer molecules, thereby producing an electronically excited sodium dimer, Na.sub.2 *. With this molecule as the upper state, a small positive gain was measured on a number of electronic transitions of the sodium dimer.
The Cobb experiment did not, however, produce a laser. Furthermore, a molecular beam device, as used by Cobb, cannot be used to generate an efficient laser, since a relatively small fraction, below 2%, of the sodium atoms are trimers. In addition, the halogen atoms cannot effectively penetrate much of the sodium vapor jet, thereby resulting in many sodium trimer molecules that pass through without reaction. There are other practical difficulties with the Cobb device, such as the 10.sup.-5 and 10.sup.-2 Torr pressure in the expansion chamber.